Carburetors of the slide and metering rod type are well known in the prior art, as evidenced by the inventor's prior U.S. Pat. Nos. 3,985,839; 4,013,741; 4,442,046; 4,221,747; 4,926,059; 4,971,730; 5,342,555; and U.S. Pat. Reissue No. 31,475. Each of these patents is hereby incorporated in their entirety by reference.
In these types of carburetors, particularly U.S. Pat. No. 4,926,059, the position of the metering rod relative to the slide member can be easily adjusted by rotation of an adjusting screw which can be engaged through an opening in the upper portion of the carburetor housing in alignment therewith. Referring to FIG. 1, this prior art carburetor is generally designated by the reference numeral 10, the carburetor comprising a body 12 having an air inlet end 14, an air outlet end 16 and a centrally located slide supporting portion 18. A cover 20 is provided to fit over the upper portion of the slide support portion 18. A fuel reservoir 21 is secured to the underside of the body beneath the slide supporting portion. Since the operation of this type of carburetor is well known, only the function of the adjusting screw will be described hereinafter.
In these types of carburetors, a throttle slide member 22 is mounted within the slide supporting portion 18 for substantially vertical slidable movement therein. The slide member 22 is actuated in a push pull manner by the control cable 24 and an actuator member 26 to control the air flow from inlet end 14 to the outlet end 16 of the carburetor body 12. The slide member 22 also controls the flow of fuel from the fuel reservoir 21 to the carburetor throat 28 because of the corresponding upward or downward movement of the metering rod 30 secured to the throttle slide member 22.
The metering rod needle 30 is adjustably secured and extends downwardly from the slide member 22 into the central opening 33 of the fuel supply tube 36. The metering rod 30 is provided with an enlarged head portion 38 which is slidably received within the complementary internal bore 40 of the slide member 22.
The position of the metering rod 30 relative to the slide 22 can be easily adjusted by rotation of an o adjusting screw or bolt 42 via the opening 44 which may be kept covered with a plug using the threads 46 therein.
The adjusting screw 42 slidably extends through an opening 48 in a plate 50 fixedly mounted within the bore 40 in the slide member 22. The end of the adjusting screw is provided with an enlarged head 52 which has a recess or the like in its upper end for receiving the end of an adjusting tool such as a screwdriver, wrench or the like.
The lower end of the adjusting screw is threadably o received within a threaded bore 54 in the head portion 38 of the metering rod 30. The head portion 38 of the metering rod is slidably received within the bore 40 in the slide member 22 and is of a size in cross-sectional shape to be complementary to the bore 40 so as to be nonrotatable therein. A coil spring 56 surrounds the adjusting screw 42 and is disposed between the lower surface of the plane member 50 and the head portion 38 to urge the metering rod 30 downwardly to a desired idle position or the like relative to the slide 22. In this manner, rotation of the adjusting screw 42 in the threaded bore 54 of the metering rod 30 causes the rod to move upwardly or downwardly in the bore 40 of the slide member. This action vertically adjusts the metering rod relative to the slide member to thereby adjust idle or mid-range operation of the carburetor.
One of the drawbacks associated with these types of adjusting screw mechanisms is that the degree of adjustment or rotation of the screw 42 can be imprecise, such impression adversely affecting carburetor operation. For example, carburetor turning instructions may require a quarter or half turn of the adjusting screw for idle or mid-range adjustment. However, since it is difficult to visually observe the rotation of the adjusting screw 42 within the slide 22, the amount of rotational displacement of the adjusting screw 42 is usually visually monitored by rotation of the adjusting screw device such as a screwdriver or the like. Thus, a person tuning the carburetor may not precisely rotate the adjusting screw to the desired quarter or half turn.
In view of the drawbacks of the prior art design as discussed above, a need has developed to provide an improved adjusting screw mechanism which provides precise and accurate adjustments through rotation for improved carburetor performance.
Responsive to this need, the present invention provides an improved carburetor adjustment screw mechanism which provides an audible signal or a sensation to indicate the degree of rotational displacement of the adjusting screw for proper carburetor adjustment.